As much time as I burn through listening to minor league games, I forget sometimes that to the vast majority of Cubs fans, the players I listen to are just names on a blog post. So here's a brief thumbnail of the left-handed pitchers in the pipeline at the top three levels.
Chris Rusin, Iowa Cubs
A fourth-round selection in the 2009 June draft, Rusin is the most ready of any of the players on this list to contribute. A finesse starter, Rusin has dropped his WHIP from the acceptable 1.3/1.4 range to a rather good 1.125 this season in the hitter-friendly Pacific Coast League. His K/9 is under six, indicating his lack of top-end velocity, but his walks are at 1.7, indicating he knows how to pitch. Lefties hit him moderately better than righties, so he doesn't profile as a specialist/LOOGY type. Rusin walked more hitters in April than he has since.
Rusin is a better pitcher now than what you saw at the end of last season. On a good team, he'd probably be a second or third lefty in the pen. He could also be a decent fourth or fifth starter, given time. The Cubs should be able to give him said time starting in late July or early August. Getting this much value from a fourth-rounder is a nice haul.
Brooks Raley, Iowa Cubs
A sixth-round selection in 2009, Raley sports a WHIP of 1.55 in Triple-A, which is up from last season. Raley fans over seven hitters per nine innings, but walks three per nine. Raley has a better ERA against lefty hitters, but is more prone to the longball by them.
Raley profiles as more of a reliever at the MLB level, but falls in line behind Rusin, regardless of the category. Raley received the first call this season, largely because filling in for a couple days in the bullpen is less of a priority (Raley) than getting in regular work (Rusin).
Hisanori Takahashi, Iowa Cubs
Takahashi has been very good in Iowa this season after being mostly awful in April in Chicago. After a bit of a slow start, he has allowed only seven hits over his last 16-and-change innings. Lefties have had better success this year against Takahashi, both in terms of power and average. He is striking out just under a hitter an inning.
If the Cubs needed another lefty in the pen to salvage the season, Takahashi wouldn't be a bad gamble. However, as he is approachng 40, he doesn't figure to advance the rebuild in terms of 2014 and beyond, or as a trade chip.
Jeff Antigua, Iowa Cubs
I saw Antigua pitch a few years back in Kane County, while he was playing in the system with Peoria. He has pitched in Low-A for each of the last five seasons. I don't see Antigua being called up, but the brass might reward him at some point for the miles logged on Midwest League buses. He is, in case you didn't guess, a soft tosser. Antigua has a low likelihood for MLB success.
Hunter Cervenka, Tennessee Smokies
Cervenka came over in the Marlon Byrd trade last season, and has exceeded expectations. He pitched for Peoria and Daytona last season, and Daytona and Tennessee this year. His Double-A numbers look a bit rough, but he was hit hard in his first two outings for the team. His last six innings for the Smokies have been scoreless. If a player can perform at Double-A, he might be able to two levels higher.
His walk and strikeout numbers are a bit on the high side generally. It's doubtful Cervenka would be selected in December's Rule 5 draft, so he will probably be able to develop another year, and may earn a call-up next season to the parent club.
Eric Jokisch, Tennessee Smokies
An 11th-round pick from Northwestern in 2010, Jokisch has steadily climbed through the system. His WHIP is normally very acceptable, helped by low walk numbers. He generally fans over 7 per nine, so he isn't a pure pitch-to-contact guy. His splits are mildly reversed, so he doesn't appear to be a specialist.
If Jokisch keeps getting people out, his long-ish shot at being a big league contributor will continue. His splits don't help him as a short reliever, but he will battle every outing. The jury is still deliberating on this verdict, which is a prudent action on most prospects anyway.
Austin Kirk, Tennessee Smokies
A third-round choice in 2009, Kirk pitched a no-hitter for Daytona on July 4, 2011. He usually sits a bit below the 7 K/9 mark, and is more finesse than flamethrower. He's also unlikely to be taken in the Rule 5 draft in December, so Kirk will have the next two years to show if he is more starter or reliever in the future. His splits are traditional, and Kirk could be a lefty specialist in a few years, though he is still a starter now.
Zach Rosscup, Tennessee Smokies
Over the winter, some Cubs prospects were invited to Chicago for a long weekend, which included attending a Blackhawks game in a club suite. Rosscup was among the invitees. Acquired with Matt Garza in the much-discussed Rays trade, Rosscup has consistently had K/9 numbers in double digits in the Cubs system. His walk numbers have been a bit up-and-down. This year, his splits are mildly reversed, but he has pitched well against all comers.
Look for Rosscup to be added to the 40-man roster this winter, if not sooner. He is probably the most likely on this list to be in an All-Star game. He will be a reliever, but since the brass likes him, he will have plenty of chances. I expect he gets a call-up in late August or September, but I hope it's late enough so the team doesn't waste an option on him as was done with Rusin and Raley last season. (There's not much point in this stage of the rebuild calling up anyone to appear once or twice, just to waste one of their three minor league options. If that is the plan, summon someone other than Rosscup, who might have future value for the team in four years.)
Kyler Burke, Daytona Cubs
Burke came over to the Cubs in 2007 from San Diego in the Michael Barrett trade. After plateauing as a hitter, he switched to the mound exclusively in 2011. His numbers in High-A have been fairly good this year, with a WHIP under 1.1, and over 8 K/9. I doubt he will ever merit a 40-man roster spot, but if he reaches (and succeeds at) Double-A, all bets are off.
Frank del Valle, Daytona Cubs
Del Valle is getting used to Daytona. That isn't necessarily what the Cubs wanted when he defected from Cuba, but he has gotten better each year in the Florida State League. After splitting time in 2012 as a starter and reliever, FDV has been exclusively a reliever this season. His K/9 is over 12. His W/9 is over 5.
While a possibility exists of del Valle reaching Wrigley, his walk numbers are disconcerting. He probably has earned a look in Double-A if a spot opens up.
Jeff Lorick, Daytona Cubs
The last-remaining vestige of the Derrek Lee trade with Atlanta, Lorick is a short-stint reliever. He has appeared in nine games in 2013, surrendering hits in his last eight. The Florida State League is hitting over .300 on Lorick. He has walked more than he has fanned this year.
Sheldon McDonald, Daytona Cubs
McDonald is very good at changing speeds on his pitches. A 33rd-round pick from Canada in 2011, McDonald has a WHIP over 1.5. He walks over four per nine innings, fanning a bit over five this season. His splits between lefty and righty hitters are rather neutral. A team can always find a role for a pitcher like McDonald, but rarely is it in the major leagues.
There are some decent left-handed pitchers in the Cubs' pipeline. None of them figure to be major players with the next good Cubs teams. Rusin, Raley, and Rosscup figure to be the best, in whichever order. None pencil in as starting pitchers in a playoff run. The bullpen figures to have a few home-grown talents over the next few years, but don't expect 95 mile per hour heat in the left-field bullpen from them in Wrigley the next few years. The team has been more interested recently in adding top-end hitting talent than adding left-handed splash in the last few years.
In other words, don't expect internally-grown southpaw stars in the next few seasons.